In this paper, crashworthiness characteristics of conical steel tubes stiffened by annular rings and rigid polyurethane foam are investigated. For this purpose, wide circumferential rings are created from the outer surface of the conical tube at some determined areas along tube length. In fact, this method divides a long conical tube into several tubes of shorter length. When this structure is subjected to axial compression, folds are shaped within the space of these annular rings. In this study, several numerical simulations using ABAQUS 5.6 finite element explicit code are carried out to study of crashworthiness characteristics of the empty and the foam-filled thin-walled conical tubes. In order to verify these numerical results, a series of quasi-static axial compression tests are performed. Moreover, load-displacement curves, deformation mechanism of the structure, energy absorption, crush force efficiency (CFE), initial peak load with different number of rings are described under axial compression. The results show that a conical tube with stiff rings as a shock absorber could be improved or adjusted the crushing mode of deformation and energy absorption ability. Manuscript profile

در این مقاله ‌، اثر آغازگر در پاسخ لهیدگی ضربه‌گیرهای شیاردار خارجی پر شده از فوم پلی‌اورتان بررسی می‌شود. به این منظور، یک آغازگر در بالای لوله استوانه‌ای شیاردار خارجی پر شده از فوم قرار می‌گیرد تا از اعمال نیروی ناگهانی به قسمت اصلی سازه جلوگیری کند. در این ایده جدید، برای مطالعه مشخصات ضربه پذیری، تعدادی شبیه‌سازی عددی در نرم افزار آباکوس به صورت شبه استاتیک انجام شده و با نتایج تجربی مقایسه می‌شود. همچنین، منحنی‌های نیرو-جابجایی و مکانیزم تغییر شکل ضربه‌گیر با تغییر تعداد شیارها توصیف می‌شود. نتایج نشان می‌دهد که وجود آغازگر باعث کاهش شدت ضربه به سازه اصلی و سرنشینان می‌شود. Manuscript profile

Cylindrical thin-walled tubes due to construction and easy installation, high energy absorption capacity are used in the automotive industry as an impact energy absorber. However, the main weakness of cylindrical tubes is in the high initial peak load. Therefore, in this paper, to overcome this weakness, a buckling initiator is used at the top of the tube. This buckling initiator is a steel rod that is installed by stretching strips at the edge of tubes. In this study, the parameters related to the initiator, including different number of pulling strips N, pre-hit height h and inclined angle of the pulling strips θ are studied. For this purpose, quasi-static simulation was conducted to determine the maximum crushing load, specific energy absorption and crush force efficiency using the software Ls-Dyna. To verify the numerical simulation, the results were compared with experimental testing. The results show that the crashworthiness characteristics and performance of the cylindrical tubes significantly improved with buckling initiator. Manuscript profile

The structural analysis of an infinite unsymmetric laminated composite Timoshenko beam over Pasternak viscoelastic foundation under moving load is studied. The beam is subjected to a travelling concentrated load. Closed form steady state solutions, based on the first-order shear deformation theory (FSDT) are developed. In this analysis, the effect of bend-twist coupling is also evaluated. Selecting of an appropriate displacement field for deflection of the composite beam and using the principle of total minimum potential energy, the governing differential equations of motion are obtained and solved using complex infinite Fourier transformation method. The dynamic response of unsymmetric angle-ply laminated beam under moving load has been compared with existing results in the literature and a very good agreement is observed. The results for variation of the deflection, bending moment, shear force and bending stress are presented. In addition, the influences of the stiffness, shear layer viscosity of foundation, velocity of the moving load and also different thicknesses of the beam on the structural response are studied. Manuscript profile